Depletion of mitochondrial DNA stabilizes C1qTNF-related protein 6 mRNA in muscle cells

Potential participation of CTRP6, a complement regulator, in the pathology of age related macular degeneration

PURPOSE

To investigate the localized expression of C1q/tumor necrosis factor related protein (CTRP) 6 in human age-related macular degeneration (AMD) retinal tissues.

EXPERIMENTAL STUDY DESIGN

4 AMD and 3 non-AMD whole eyes of Caucasian donors were used. Eyecups were excised at Eye Bank CorneaGen, Inc.

METHODS

To elucidate the effects of CTRP6, C3b was measured by an enzyme-linked immunosorbent-like assay. CFB versus CTRP6 competitive binding assay was applied to clarify the inhibition by CTRP6 of C3bBb complex formation. The cornea, iris, lens, and vitreous were removed and the eyes were cut into a posterior eye-cup including the retina, choroid, and sclera. Six-µm-thick serial sections of frozen samples underwent hematoxylin-eosin (HE) staining and indirect immunohistochemical staining using primary antibodies, anti-CTRP6, -CTRP5, -CTRP10, -Complement factor H (CFH) and -Clusterin (CLU). Results The two in vitro studies confirmed that CTRP6 has an inhibitory effect on alternative pathways of complement (APC) function and that the molecular target of CTRP6 is the inhibition of the formation of C3bBb. Localized expression for CTRP6 and CFH was found in the drusen of the AMD eyes, both associated with APC inhibition, CLU associated with membrane-attack complex (MAC) inhibition, and CTRP5 associated with retinal degeneration.

CONCLUSION

The localized expression of CTRP6 in the drusen of AMD eyes may open a new insight into the possible involvement of APC regulatory factors in the pathogenesis of AMD, together with the known CFH so far analyzed solely as an APC inhibitor.

C1QTNF6 Overexpression Acts as a Predictor of Poor Prognosis in Bladder Cancer Patients

Background

Bladder cancer is one of the most common urinary malignancies. This study is aimed at providing some promising molecular biomarkers for bladder cancer (BC) by investigating the correlation between C1QTNF6 expression and clinical characteristics as well as prognosis in patients with bladder cancer.

Methods

Sequencing profiles of C1QTNF6 mRNA in BC patients were collected to evaluate the distinctive gene expression, between normal bladder mucosa and BC, according to the TCGA and GEO databases. The association between C1QTNF6 expression and the clinical features as well as the disease prognosis was evaluated using two independent cohorts. The expression of C1QTNF6 in normal bladder and BC cells was examined by western blotting and PCR, so the underlying molecular mechanism could be further investigated.

Results

C1QTNF6 mRNA levels were found to be differentially expressed in two independent public cohorts, including the TCGA database and GSE13507 dataset from GEO. The protein and RNA levels of C1QTNF6 in BC cells were both elevated when compared to normal bladder cell lines. High C1QTNF6 expression was detected in advanced T/M stages, pathological grade, and AJCC stage when compared to the low C1QTNF6 expression group. The underlying mechanism related to this differential expression could be explained by cell migration and invasion assays, where bladder cancer cells 5637 and T24 had a significant reduction on migration and invasion ability upon knockdown of C1QTNF6 expression. The low C1QTNF6 expression group presented a more prominent OS advantage over the high-expression group in both TCGA and GSE13507 cohorts. Moreover, the protein content in tissues was further validated using the HPA database and TMA. Survival analyses also indicated that the high C1QTNF6 expression group had an unfavorable OS when compared to the low-expression group.

Conclusions

High C1QTNF6 expression may serve as a predictor of poor prognosis in bladder cancer patients, and the underlying mechanism is possibly associated with changes on cancer cell migration and invasion ability.

Circulating levels of C1q/TNF-α-related protein 6 (CTRP6) in polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is one of the most common endocrine disorders affecting females of reproductive age. It has been associated with cardiometabolic disorders including diabetes mellitus and cardiovascular disorders, and increases the risk of developing fecundity pathologies including recurrent pregnancy loss (RPL) and infertility. C1q/tumor necrosis factor-α-related protein-6 (CTRP6) is a novel adipokine involved in glucose and lipid metabolism, host inflammation, and organogenesis. In the present study, we aimed to determine the association of serum CTRP6 levels with some components of metabolic syndrome in PCOS patients (infertile PCOS [inf-PCOS] and PCOS-RPL). This case-control study included 120 PCOS patients (60 inf-PCOS and 60 PCOS-RPL) and 60 healthy controls. Serum high-sensitivity C-reactive protein (hs-CRP) and homocysteine were measured using commercial kits, while adiponectin and CTRP6 levels were assessed using ELISA technique. Inf-PCOS and PCOS-RPL individuals had higher levels of serum CTRP6 than controls (546.15 ± 125.02 ng/ml and 534.04 ± 144.19 ng/ml vs. 440.16 ± 159.24 ng/ml; both p < .001). Moreover, serum adiponectin levels were significantly reduced, while fasting insulin, homeostasis model assessment of insulin resistance, free testosterone, and hs-CRP levels were significantly elevated in PCOS group, when compared with controls. Furthermore, serum CTRP6 positively associated with body mass index in all subjects. It showed an inverse correlation with adiponectin in PCOS group and subgroups. However, it had a direct association with hs-CRP in PCOS group and inf-PCOS subgroup, but not PCOS-RPL subgroup. These findings unravel a probable role of CTRP6 in PCOS pathogenesis, which poses a possibility to be a good diagnostic target. However, further investigation is needed.

CTRP6 Regulates Porcine Adipocyte Proliferation and Differentiation by the AdipoR1/MAPK Signaling Pathway

Intramuscular fat (IMF) and subcutaneous fat (SCF), which are modulated by adipogenesis of intramuscular and subcutaneous adipocytes, play key roles in pork quality. C1q/tumor necrosis factor-related protein 6 (CTRP6), an adipokine, plays an important role in the differentiation of 3T3-L1 cells. However, the effect and regulatory mechanisms of CTRP6 on porcine adipogenesis, and whether CTRP6 has the same effect on intramuscular and subcutaneous adipocytes, are still unknown. Here, we found that CTRP6 significantly inhibited both adipocyte proliferation assessed by proliferative marker expression, but CTRP6 decreased the proliferation rate of intramuscular adipocytes (IM) to a greater extent than subcutaneous adipocytes (SC). Moreover, CTRP6 promoted the activity of the p38 signaling pathway during the proliferation of both cell types. Nevertheless, in subcutaneous adipocytes, CTRP6 also influenced the phosphorylation of extracellular regulated protein kinases1/2 (p-Erk1/2), but not in intramuscular adipocytes. Additionally, during the differentiation of intramuscular and subcutaneous adipocytes, CTRP6 increased adipogenic genes expression and the level of p-p38, while it decreased the activity of p-Erk1/2. Interestingly, the effect of CTRP6 shRNA or CTRP6 recombinant protein was attenuated by U0126 (a special p-Erk inhibitor) or SB203580 (a special p-p38 inhibitor) in adipocytes. By target gene prediction and experimental validation, we demonstrated that CTRP6 may be a target of miR-29a in porcine adipocytes. Moreover, AdipoR1was identified as a receptor of CTRP6 in intramuscular adipocytes, but not in subcutaneous adipocytes. On the basis of the above findings, we suggest that CTRP6 was the target gene of miR-29a, inhibited intramuscular and subcutaneous adipocyte proliferation, but promoted differentiation by the mitogen-activated protein kinase (MAPK) signaling pathway. These findings indicate that CTRP6 played an essentially regulatory role in fat development.

Lipogenesis in myoblasts and its regulation of CTRP6 by AdipoR1/Erk/PPARγ signaling pathway

The induced lipogenesis and its regulation in C2C12 myoblasts remain largely unclear. Here, we found that the cocktail method could significantly induce lipogenesis through regulating lipid metabolic genes and Erk1/2 phosphorylation in myoblasts. Meanwhile, the expression and secretion of CTRP6 were increased during ectopic lipogenesis. Moreover, CTRP6 knockdown down-regulated the levels of lipogenic genes and phosphorylated Erk1/2 (p-Erk1/2) in the early lipogenic stage, whereas up-regulated p-Erk1/2 in the terminal differentiation. Interestingly, the effect of CTRP6 siRNA was attenuated by U0126 (a special p-Erk1/2 inhibitor) in myoblasts. Furthermore, AdipoR1, not AdipoR2, was first identified as a receptor of CTRP6 during the process of mitotic clonal expansion. Collectively, we suggest that CTRP6 mediates the ectopic lipogenesis through AdipoR1/Erk/PPARγ signaling pathway in myoblasts. Our findings will shed light on the novel biological function of CTRP6 during myoblast lipogenesis and provide a hopeful direction of improving meat quality of domestic animal by lipogenic regulation in skeletal muscle myoblasts.

Knockdown of CTRP6 inhibits adipogenesis via lipogenic marker genes and Erk1/2 signalling pathway

C1q/tumor necrosis factor-related protein 6 (CTRP6), an adipose-tissue secretory factor, plays an important role in inflammatory reaction and carcinogenesis. However, the biological function of CTRP6 in adipogenesis remains unclear. In this study, we examined the effects of CTRP6 knockdown on lipogenesis of 3T3-L1 adipocytes. The results showed that after 3T3-L1 adipocytes transfected with anti-CTRP6 small interfering RNA (siRNA), not only levels of secreted CTRP6 protein in the culture medium but also the expression level of the CTRP6 protein in the 3T3-L1 adipocytes was significantly reduced (P < 0.01). In addition, the number of lipid droplets in the adipocytes was reduced, as well as the OD values reflecting the fat content being significantly decreased (P < 0.01). Meanwhile the levels of adipogenic markers, including peroxisome proliferator activated receptor γ (PPARγ), CCAAT/enhancer-binding protein α (C/EBPα), CCAAT/enhancer-binding protein β (C/EBPβ) and adipocyte fatty acid-binding protein 4 (aP2), were decreased after treatment with anti-CTRP6 siRNA, whereas the expression of adipose triglyceride lipase (ATGL) and triacylglycerol hydrolase (TGH) were increased. Furthermore, after transfection, activity of phosphorylated Erk1/2 (p-Erk1/2) was inhibited in the early stage of differentiation, but in terminal differentiation of adipocytes, its activity was activated. Taken together, the results indicate that knockdown of CTRP6 can inhibit adipogenesis of 3T3-L1 adipocytes through lipogenic marker genes and Erk1/2 signaling pathway.